3 Answers
3

There's two ways to adjust the toe in. The metal pad holders that are the other half of the brake pad assembly should have some semispherical washers in them, allowing you a few degrees of adjustment. Loosen the bolt that holds it on, jiggle it to free up all the pads, then squeeze the brake lever to pull the pad against the rim and get the alignment right. Using a wee bit of cardboard or something between pad and rim at the back to set the toe in, of course.

The other method is to carefully bend the caliper/brake arm. Obviously it's much better to use the previous method, but if that's not an option, set an adjustable wrench so that it fits tightly onto the slotted part of the arm (just above the brake pad), and twist the arm to a better position. Careful is the word - much better to have to tweak it three or four times than have to bend it back if you go too far.

There are no such semi-spherical washers....
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Billy ONealJul 4 '11 at 4:31

There are. I can see them in the picture. Unless that isn't your bike? They don't look like they offer adjustment, but they do.Try tightening the brake pad fixing bolt just enough so that you can fell a little tension on the bolt. Then grab both ends of the pad holder, and try moving it in the plane of the change you're having trouble with. It should move, if a little stiffly. I would leave the bending of the arm adjustment to a shop, unless you are very confident. It's a legit technique, Park even makes a tool just for that, but it can cause permanent damage to the brake if done badly.
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zenbike♦Jul 4 '11 at 5:08

Make sure that the washers don't have a wee tab out one side, to allow you to rotate them as they are wedge-shaped.
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МסžJul 4 '11 at 5:09

Although that isn't usually the case with any Shimano brake, if it is here, then your best option is to replace the pad holders with a new set. You can buy a 105, or Ultegra level pad with the holders and the adjustment washers for around 50 USD a set. This appears to be a Trek 1500, from around 2003-2004 based on the fork and the graphics. Should have 9 speed Tiagra components? Is that correct?
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zenbike♦Jul 4 '11 at 6:27

Sorry, I wasn't going to post this as an answer, but I couldn't post the photo otherwise.
Credit goes to @Moz

There are adjustment washers. I can see them in the picture.

Unless that isn't your bike? They don't look like they offer adjustment, but they do.Try tightening the brake pad fixing bolt just enough so that you can feel a little tension on the bolt. Then grab both ends of the pad holder, and try moving it in the plane of the change you're having trouble with. It should move, if a little stiffly. I would leave the bending of the arm adjustment to a shop, unless you are very confident. It's a legit technique, Park even makes a tool just for that, but it can cause permanent damage to the brake if done badly.

It does not move. Those washers are both flat -- tightening those bolts always aligns the brake pads the exact same way. I have seen the kind of semispherical setups both you and @Мסž are talking about, but this bike is not equipped with those. (The rear shoes don't even have a washer of any type on that side of the caliper)
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Billy ONealJul 4 '11 at 6:08

Did you try to move it as I suggested, or are you assuming that it won't move because it looks flat?
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zenbike♦Jul 4 '11 at 6:30

Yes, I tried that before posting here. Tightening down that screw always undoes any positioning you have done to the pad (beyond moving up and down the caliper arm itself of course)
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Billy ONealJul 4 '11 at 8:04

Then you're left with replacing the pad holders, or bending the arm. Since I know that brake is intended to have adjustable holders, I'd start by replacing them with new ones.
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zenbike♦Jul 4 '11 at 8:07

I suspect that the spherical washers are there, just frozen to the brake arms so they won't move (aluminum sticks to aluminum). You can try completely disassembling one of them to examine the washers.

But the "uneven" wear you show in your first picture is actually fairly even -- I'd be happy with that. And, aside from the first millimeter or so, "toe-in" won't affect brake pad wear substantially. If your pads are wearing out rapidly it's likely due to some other issue -- poor quality pads (or just the wrong ones for your use), rough rim surface, etc.

Keep in mind that pads are available in several different hardnesses, from soft and "grabby" to so rock-hard that you have to be a gorilla to squeeze the things. Generally, the softer the pad, the faster it will wear.

I did completely pull off the shoes in order to replace the pads. There was no such washer assembly.
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Billy ONealJul 4 '11 at 18:09

The wear in that picture is consistent, but clearly not a properly adjusted brake. Left unchecked, the metal pad holder would soon be digging into the rim. I do agree with the fact tat once the rubber is flat on the rim, wear will be no different than the correctly adjusted pad, but that is no reason not to fix it.
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zenbike♦Jul 5 '11 at 10:21

You're never going to get it perfect, and those pads are a long way from hitting the rim. Keep in mind that only a cantilever applies "perfectly" symmetrical force. There will always be a little imbalance in the arms of other brake styles -- one arm will move a little faster, and one arm will flex more.
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Daniel R HicksJul 5 '11 at 11:30